For those out there that have a light colored rubrail on their boat that is full of skuffs and marks from docks/bumpers there is hope..
When I bought my boat the rail was in pretty rough shape from the bumpers the previous owners used. The solution: Acetone and a rag. Soak a portion of the rag in acetone and everything will come right off. It takes some elbow-grease and sometimes a few passes around the boat but will come out looking like new. I found that the more acetone on the rag, the easier it was to remove the skuffs. Hope you all can benefit from this post!